1. Field of the Invention
This invention relates broadly to intraluminal vascular implant devices. More particularly, this invention relates to intraluminal stents and grafts.
2. State of the Art
An abdominal aortic aneurysm (AAA) is a sac caused by an abnormal dilation of the wall of the descending aorta as it passes through the abdomen. The aorta is the main artery of the body, supplying blood to all organs and parts of the body except the lungs. It is typically described as three parts: the ascending aorta which rises upward from the left ventricle of the heart, the aortic arch which bends over to extend downward; and the descending aorta which passes down through the thorax and through the abdomen and finally divides into the two iliac arteries (which supply blood to the pelvis and lower extremities).
The aneurysm ordinarily occurs in the portion of the aorta below the kidneys. When left untreated, the aneurysm will eventually cause the sac to rupture with ensuing fatal hemorrhaging in a very short time. The repair of abdominal aortic aneurysms has typically required major abdominal surgery in which the diseased and aneurysmal segment of the aorta is removed and replaced with a prosthetic device, such as a synthetic graft.
As with all major surgeries, there are many disadvantages to the foregoing surgical technique, the foremost of which is the high mortality and morbidity rate associated with surgical intervention of this magnitude. Other disadvantages of conventional surgical repair include the extensive recovery period associated with such surgery; difficulties in suturing the graft to the aorta; the loss of the existing thrombosis to support and reinforce the graft; the unsuitability of the surgery for many patients, particularly older patients exhibiting co-morbid conditions; and the problems associated with performing the surgical procedure on an emergency basis after the aneurysm has already ruptured.
In view of the foregoing disadvantages of conventional surgical repair, catheter-based techniques have been developed for repairing abdominal aortic aneurysms by delivering an aortic stent graft to the aneurysm site via a catheter, and expanding the stent such that it secures the graft within the aorta. Stent grafts have been developed in order to not only simply hold open a passageway, but also to bridge across diseased vasculature from healthy vessel to healthy vessel.
Briefly, a stent graft is inserted over a guide wire, from the femoral or iliac artery and deployed within the aneurysm by a catheter, resulting in maintenance of blood flow from an aorta of acceptable (usually normal) caliber above to a portion of aorta or iliac artery(s) of acceptable (usually normal) caliber below the aneurysm. The aneurysm sac is thus excluded. Blood within this excluded sac thromboses and the aneurysm thus has no flow within it, presumably reducing the pressure and thus its tendency to burst.
Presently available stent grafts however have a number of problems. For example, current stent grafts are prone to persistent leakage around the area of the stent graft. Hence, pressure within the sac stays at or near arterial pressure and there is still a risk of rupture. There are 3 common types of such leakage. The first type is direct leakage around the stent graft. This can be persistent from the time of insertion because of poor sealing between the stent graft and vessel wall, or can develop later because the seal is lost. In addition, this problem can develop because the stent graft is not adequately fixated within the descending aorta, which allows the stent graft to migrate in relation to the aneurysm as the aneurysm grows, shrinks, elongates or shortens with time after treatment. The second type of leakage can occur because there are side arteries extending out the treated segment of blood vessel. Once the aneurysm is excluded by the device, flow can reverse within these blood vessels and continue to fill the aneurysm sac around the stent graft. The third type of leakage is direct leakage through the graft. Such leakage can occur in devices that use extensive amounts of metal in the stent and/or sutures to affix the graft to the stent. In these devices, the metal and/or sutures can abrade causing a rupture in the graft and leakage therefrom. Modular devices typically have connections that rely on friction alone. Such connects can disarticulate, thus causing leakage therefrom.
Some of the presently available stent grafts are also limited in their application to only select patients due to limitations in their design, including:
limited flexibility—which can cause difficulties during delivery and possible incompatibility for patients with a tortuous iliac artery, a tortuous aorta, and/or a tortuous aneurysm;
limited conformity with changing aneurysm shape—which can cause leakage;
required infrarenal fixation (i.e., fixation below the renal arteries)—which results in incompatibility for patients with a short infrarenal neck (i.e., a relatively short distance of healthy vasculature below the renal arteries);
limited sizes—which results in incompatibility for patients with an aneurysm size different from such limited size; and/or
required delivery by a large diameter catheter—which results in incompatibility for patients with an iliac artery and/or aorta that is tortuous or possibly heavily calcified and diseased (which are frequently associated with AAA).
Thus, there remains a need in the art for an improved stent graft that does not suffer from the limitations of the prior art designs.